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What do you do when you can’t lift those heavy rocks but you want ‘big’ rocks? You knew I was going to say; ‘make them’! Here’s how to make your own Lightweight Concrete faux Rock.

When you get a ‘new’ TV:

When you get a new appliance and look at that mountain of styrofoam; there must be something I can do with it?! I heave been saving it for a while… and hubby was bugging me to get rid of it, soooo…

I like large rocks; diamonds and the like, the bigger – the better. I know rocks are cumbersome and back-breaking, so light weight ones are a dream. That’s when my problem-solver brain brought a few methods together.

I wanted to keep this as simple as possible. I did not want to fight with that chicken wire that always seems to poke & hook my skin. Simple – just attach a random shape of pieces of styrofoam. Wear gloves so you won’t be sticking to everything. I did not break many pieces as I hate the way it starts to cling and get everywhere.

Styrofoam does not absorb water, It’s light and pretty sturdy as well; so perfect as a form. Many glues will dissolve the styrofoam, so I found a can of ‘Great Stuff’ (as I was also incidentally also doing some window trim repair) It works well to attach the styrofoam as it quickly starts to set and also fills gaps. I was not fussy at all, just stuck random pieces together since I do not like the round rocks; I much prefer rocks with angles, textures and layers. There is another step for more detail so this is just a basic starting shape.

I was amazed at how quickly they all came together. I had 3 big bags full of pieces!

Base forms made!

These range about 18″ to 30″ in size. It’s ok to have a bit of flat sides as natures rocks often break off in layers as well.

Messy hands time!

I have used draping of concrete soaked fabric for a few projects now. The (famous) Spook, The Faux Bois Chair, the Cat and even the Rope Orbs all have some part of this method. So I realized that it would make for a great way to get a base shape, a stiff concrete skin.

My favourite way is to use only portland cement as it gets really smooth and can absorb well into fibres. Since I have a lot of used flannel from Eco printing, I found that it works well. It is a bit thinner but nicley absorbent. No problem to have extra layers or wrinkles either.

To make it less messy (a bit) I used smaller pieces, not really sized at all. ‘Think of it like paper-maché, layer and smooth out.

I found trying to wrap all the way around was a problem, as it would fall off. So I only did the tops and sides and then let cure. Remember, do not let it dry out too fast. Misting with water does not hurt, it helps.

I know they look strange, bit it’s just a base shape… you can be fussier if you like but usually the more contrived then the less it looks like nature..

Once the tops and sides are cured (usually overnight) you can wrap the bottom and even up the sides if it’s weak. There will be another layer so a few weak spots are not really an issue. It all depends also where you plan to put these. Mine are going to make a waterfall structure, not be climbed on. If you want them pretty indestructible, add more layers of the cement soaked fabric. If you choose thicker fabric it tends to get stiffer since more cement is impregnated, but also uses more mix. See my tests here.

These still look a bit boxy but looking pretty good considering how easy they were so far!

Some simple Tools:

To make some rock-like texture some simple tools can be used. An old brush dipped in a bit of fast setting cement or whatever else can make some good pebbly divots. Knives, like putty or pallet knives help spread the next layer, trowels help apply as well.

When adding any new concrete to existing it needs to be wetted, and if you want extra reassurance a bonding layer with a Bonding Agent can be painted on. I generally don’t use it bit did try for a couple to compare in the future.

The Second Concrete Layer

To make the texture and detail layer is made with Rapidset Mortar Mix. I have used their other product for many things so I trusted this one as well. It feels sandier than the Rapidset Cementall which makes better texture for rocks! BEWARE – it does set really fast! So use small quantities.

Add handfulls, some lumps, some divots, some crack lines… Dab with brush for texture. If needed google images of rocks. If you overthink it, they look more contrived.

Even corners are ok, as quarry stone is broken in big blocks.

The palette knife lets you form the concrete like icing a cake. These rocks will become a waterfall so the top layer was to be more like split layered rock. It’s quite fun to make random ledges, cut some cracks and roughen the edges. HOWEVER, do not get too much small detail! You will notice that small detail generally gets lost from a distance.

As it starts to set it can be carved into to make crisp cracks or crumbly edges.

The Question about Colour

As an illustrator I know that rocks are not just grey. They have many undertone colours. It also depends where your rocks will be, are they going with other natural rocks? Even some areas have different tendencies of colour. I knew I may need some adjustment later on (it’s the artist in me) but for now I added some black concrete colour watered down and worked into the areas that would naturally get darker. Vertical areas usually get darker as well as cracks. It is tricky since it will dry different later.

Keep things damp; the spray bottle handy – it allows the colour to flow naturally into crevices.

You can mix some of the concrete colour into some of the mix as well and spread on. Colours changes are usually not that pronounced, they look more like ‘dirty’ parts of rocks. I bet there will be some natural darkening as mossy areas will develop from being in a woodland setting

Texture is one of the most convincing parts of a rock. Don’t make it look like an ‘iced cake’

Have fun and ‘Rock on’!

Stay tuned to see how the waterfall all came together! There’s also a bit of a surprise since it’s the habitat for a certain ‘friend’ of mine…

barbmaker

I'm an artist & I make things... all kinds of things.

This Post Has 21 Comments

    1. In that case, I would make sure they are pretty thick since things like lawn mowers may run into it. A couple layers of the cement-dipped fabric would make it stronger. Yes, there are endless possibilities!

      1. Love this. Just threw out foam from TV last week. UGH.

        I have made 1/2 dozen concrete people. An original from you, a bird lady- used gloves and put a bluebird in her hands, Jamaican IRE man… and on & on.

        A trick / tip for you.

        Regular wood stain works well on concrete. So does oil paint in the tube. I have put it direct and diluted. So easy. It is absorbed right into the concrete.
        You need to do it after set, but before dry so it will be absorbed.

        Hope you find this helpful.
        Fun to be had by all.

        1. So you must ave a yard like mine with odd concrete creatures! Interesting about the wood stain. I always thought oil base paint would be brittle but maybe the key is that it is IN the concrete. Many colour additives are quite pricey for the crafter. I am sure the concrete will become more and more aged as it is exposed to the elements… Yup fun stuff.

  1. I LOVE THIS AS WE LIVE IN THE WOODS YES IN THE WOODS AND WE LOVE HERE AND WE ARE ON A 9 MILE LAKE WITH LOTS OF ROCKS NOW WERE TO START .LOL I THINK I’LL DO SOMETHING LIKE THIS NEAR THE WATERS EDGE NOT SO FAR TO CARRY THE ROCKS . WE COULD HOOK UP A PUMP FOR THE WATER FALL.. I CAN’T WAIT .

  2. Barb – when future geographical excavations are done, nobody is going to be able to figure out what is what and they might be well sent down the garden path trying to sort it all out! Love this project. Seriously, your husband had to be very impressed by now and looking forward to what you’ll be getting up to next. Amazing stuff.

    1. Thanks! I even thought of making a rock planter of sorts… Sometimes I wish I could turn off the brain! Everyone around here is used to all my shenanigans!

  3. Hello Barb,
    Have you ever used rapidset mortar mix in any of your castings?
    I have tried it in a couple of smaller statues and really liked the look. Sets in -15 min.
    Hope it holds up in the elements?
    Arenda

    1. No, this is my first use. I had used another mortar mix mistakingly and it did not fair well. But I am liking this one! Yes, super fast, almost too fast! ‘But that makes you not fuss so much; a good thing.

  4. Barb
    You are Simply Amazingly Talent !!
    WOW I just am So Excited to Try this Out !!
    Thank You, Chris

  5. I love what your imagination and creativity turn out such amazing projects! Thank you for inspiring me!

  6. Barb, what did you do with the dead space under the rocks? Did you make a scaffolding to keep it elevated?

  7. Barb, I have been making faux rocks for a while now and been fighting with the chicken wire, as you said…but that seems to be the standard way in all online tutorials.
    I am thrilled to see your flannel option, but that’s just like you. Always thinking outside the box.
    Like you, I save many things that I think will be useful later…so I have plenty of Styrofoam just waiting for its chance to debut.
    You’re a gem, thank you all your posts, I know it takes a lot of your time to create, take pictures and then post it all…but is greatly appreciated by so many people.
    BTW, I am 76 and still loving to be outside playing in concrete.
    Hugs to you my friend….

    1. I appreciate that you understand the work. My brain and body are somewhat not at the same speed… 76?! I am so impressed! Maybe my new knees will make things better & faster! Thanks my friend!

  8. You have just save me so much time and experimentation. I’ve being trying to use Styrofoam, cement and fabric to make fake rocks. Trouble is foam is hard to manage when tied together with baling twine. The next attempts were going to be with wire or PVA glue ( Aussie for white/wood? glue) My dog found a mouse nest inbetwen the layers when I left it uncemented too long. So gaps, not ideal.
    Thanks heaps for sharing
    Rae

    1. When attaching styrofoam some glues will dissolve it, others won’t dry as the styrofoam does not let air get to it. I like to use this site for help when attaching odd materials. And those pesky mice are quite resourceful!

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